This paper investigates the impact of surface finish on the reliability of flip chips assembled to printed circuit boards (PCB). Two immersion silver (Ag) finishes and one electroless nickel/immersion gold (NiAu) finish were used in the study. A series of extended reliability tests, including thermal cycle, high temperature storage (HTS), and high temperature operating life (HTOL), were conducted to reveal the wear-out mechanisms of the flip chip system. Three failure mechanisms, namely under bump metallurgy (UBM) consumption, solder electromigration, and solder fatigue, were observed in HTS, HTOL, and thermal cycle tests respective y. Flip chips with Ag board finish had substantially higher reliability than those with NiAu finish, particularly in HTS and HTOL tests. Gold induced UBM consumption and solder embrittlement had significantly reduced the reliability of flip chips assembled to boards with NiAu finish.
展开▼
